Granular Fibre-Free Microporous Thermal Insulation Material and Method

ABSTRACT

A granular fibre-free microporous thermal insulation material, having a thermal conductivity less than 0.05 W/mK and a shrinkage of not more than 10%, which is free flowing and consists of granules of an intimate mixture of: 30-95% dry weight microporous insulating material; 5-70% dry weight infrared opacifier material; 0-50% particulate insulating filler material; and 0-5% binder material. The material is made by mixing together the microporous insulating material and the infrared opacifier material to form an intimate aerated mixture with a first density; conveying the intimate mixture at a first volumetric flow rate to an extrusion means ( 5 ); extruding the intimate mixture as a compressed material with a second density greater than the first density at a second volumetric flow rate lower than the first volumetric flow rate; venting a proportion of air from the aerated intimate mixture through a porous membrane to relieve pressure generated within the intimate mixture due to the change from the first volumetric flow rate to the second volumetric flow rate; and granulating the compressed material.

The present invention relates to granular fibre-free microporous thermalinsulation material. The invention also relates to a method ofmanufacturing granular fibre-free microporous thermal insulationmaterial.

The term “microporous” is used herein to define porous or cellularmaterials in which the ultimate size of the cells or voids is less thanthe mean free path of an air molecule at NTP, i.e. of the order of 100nm or smaller. A material which is microporous in this sense willexhibit very low transfer of heat by air conduction (that is, collisionsbetween air molecules). Such microporous materials can be obtained fromcontrolled precipitation from solution, the temperature and pH beingcontrolled during precipitation to obtain an open lattice precipitate.Other equivalent open lattice structures include pyrogenic (fumed) andelectro-thermal types in which a substantial proportion of the particleshave an ultimate particle size less than 100 nm. Any of these materials,based for example on silica, alumina or other metal oxides, may be usedto prepare a composition which is microporous as defined above.

In order to provide insulation for certain high temperature applicationswhich restrict the use of sheets or blocks of insulating material (forexample pipe-in-pipe insulation, such as for exhaust pipe systems,furnace cavities, double skin linings, areas over arched roofs, openjoints and for levelling furnace bottoms and hearths) loose filledthermal insulation material can be used.

In order for loose filled thermal insulation material to be efficient,it is necessary for the insulation material to be relatively freeflowing such that the individual pieces of insulation material do notundergo cohesion and bridge across gaps. Pieces of free flowing thermalinsulation material need to be able to move past each other to enablethe insulation material to settle into the most dense packingarrangement possible and thus avoid uninsulated areas being formed.Granulation is well known to make materials made from fine particlesflow relatively more easily.

Sheets or blocks of microporous insulation materials are known to havesubstantially superior thermal conductivity properties than otherinsulation materials due to the size of the voids as describedhereinbefore.

Granular insulations contain relatively large voids (greater thanmicroporous voids as defined hereinbefore) between successive granularpieces of the insulation which causes the thermal conductivity of thegranular material to be high relative to large continuous bodies ofcomparable insulation. As such, granular microporous thermal insulationmaterials are not generally available as any thermal insulationadvantage gained by the individual granules of microporous insulationhaving the microporous voids is lost due to the large voids between thegranules. The large voids in granular microporous thermal insulationsare caused in part by the presence of reinforcing fibres within thegranules. The fibres make the granules “hairy” and as such the abilityto close pack the granules is reduced.

Granular microporous aerogel materials are known, for example grade IN01beads from Cabot sold under the registered trademark NANOGEL. However,such thermal insulation materials undergo relatively high shrinkage onheating. For example the height of the NANOGEL granular aerogel materialwithin a crucible, measured before and after heating for 24 hours,decreases by 12 percent following heating at 600 degrees Celsius and by24 percent following heating at 800 degrees Celsius.

Granular forms of non-microporous thermal insulation material with goodfree flowing properties are known.

Vermiculite granules, for example exfoliated fine grade vermiculitesupplied by Skamol of Denmark, have a relatively high thermalconductivity at a density of nominally 150 to 180 kg/m³, for example0.105 W/mK at a mean temperature of 200 degrees Celsius and 0.145 W/mKat a mean temperature of 400 degrees Celsius.

Other forms of granular free flowing thermal insulation material arebased on granulated mixtures of clay and calcined diatomaceous earth,for example Moler 05 aggregate supplied by Skamol of Denmark. Theseinsulation materials also have relatively high thermal conductivity, forexample 0.2 W/mK at a mean temperature of 200 degrees Celsius.

It is an object of the present invention to provide a granularfibre-free microporous thermal insulation material, and a method ofmanufacture thereof, which is free flowing, resistant to hightemperatures and which has relatively low thermal conductivity.

According to one aspect of the present invention there is provided agranular fibre-free microporous thermal insulation material, having athermal conductivity less than 0.05 W/mK and a shrinkage of not morethan 10%, which is free flowing and consists of granules formed from anintimate mixture of:

-   -   30-95% dry weight microporous insulating material,    -   5-70% dry weight infrared opacifier material,    -   0-50% particulate insulating filler material, and    -   0-5% binder material.

According to another aspect of the present invention there is provided amethod of manufacturing a granular fibre-free microporous thermalinsulation material, having a thermal conductivity of less than 0.05W/mK and a shrinkage of not more than 10%, which is free flowing andconsists of granules formed from a mixture of 30-95% dry weightmicroporous insulating material, 5-70% dry weight infrared opacifiermaterial, 0-50% particulate insulating filler material, and 0-5% bindermaterial comprising the steps of:

-   -   mixing together the microporous insulating material and the        infrared opacifier material to form an intimate aerated mixture        with a first density;    -   conveying the intimate mixture at a first volumetric flow rate        to an extrusion means;    -   extruding the intimate mixture as a compressed material with a        second density greater than the first density at a second        volumetric flow rate lower than the first volumetric flow rate;    -   venting a proportion of air from the aerated intimate mixture        through a porous membrane to relieve pressure generated within        the intimate mixture due to the change from the first volumetric        flow rate to the second volumetric flow rate; and    -   granulating the compressed material.

The first volumetric flow rate may be in a range from 2.0 to 4.5 timesthe second volumetric flow rate.

The first volumetric flow rate may be in a range from 100 to 300litres/hour, preferably in a range from 125 to 280 litres/hour.

The second volumetric flow rate may be in a range from 20 to 90litres/hour, preferably in a range from 25 to 90 litres/hour.

The intimate mixture may be screw conveyed to the extrusion means.

The intimate aerated mixture may be extruded by at least one roller,preferably a pair of opposing rollers.

A pressure in a range from 2.5 to 20 bar, preferably in a range fromsubstantially 5 to substantially 10 bar, may be exerted on the intimateaerated mixture.

The porous membrane may be metallic and may have pores with nominaldiameters in a range from 5 to 50 microns, preferably substantially 15microns.

The compressed material may be in the form of a sheet of compressedmaterial.

The compressed material may be broken up into smaller pieces prior tobeing granulated, for example by rotary chopping.

Granulation of the compressed material may include the step of forcingmaterial through apertures in a mesh, preferably a metal mesh, using arotor.

The granular fibre-free microporous thermal insulation material may havesubstantially the following composition:

-   -   40-85% dry weight microporous insulating material,    -   15-60% dry weight infrared opacifier material,    -   0-50% particulate insulating filler material, and    -   0-5% binder material.

The granule size of the granular fibre-free microporous thermalinsulation material may be in a range from 0.25 mm to 2.5 mm.

The bulk density of the granular fibre-free microporous thermalinsulation material may be in a range from 180 to 350 kg/m³.

The tap density of the granular fibre-free microporous thermalinsulation material may be in a range from 250 to 450 kg/m³.

The opacifier material may be selected from titanium dioxide, irontitanium oxide, zirconium silicate, zirconium oxide, iron oxide, siliconcarbide, and mixtures thereof.

The microporous insulating material may comprise silica, for examplefumed and/or precipitated silica.

The fumed silica may have a BET specific surface area in a range from180 m²/g to 230 m²/g, more preferably nominally 200 m²/g.

The fumed silica may have a hydrophobic surface treatment.

The particulate insulating filler material may be selected fromvermiculite, perlite, flyash, volatilised silica, and mixtures thereof.

The binder may be an organic binder, for example polyvinylalcohol, ormay be an inorganic binder, for example selected from sodium silicate,potassium silicate, aluminium orthophosphate, and mixtures thereof.

For a better understanding of the present invention and to show moreclearly how it may be carried into effect reference will now be made tothe following examples, and to FIG. 1 which is a schematic illustrationof a method of producing a granular fibre-free microporous thermalinsulation material in accordance with the present invention.

EXAMPLE 1

A series of three granular fibre-free microporous thermal insulationmaterials (Mix Nos. 1 to 3) were made by mixing together a mixture ofnominally 60% dry weight of a microporous insulating material in theform of fumed silica material available from Degussa AG under theRegistered Trade Mark AEROSIL A200, and 40% dry weight of infraredopacifier in the form of rutile (titanium dioxide), available fromEggerding Group, Amsterdam to form intimate, homogenous aeratedmixtures. The aerated mixes had a bulk density of 80 kg/m³.

The fumed silica had a nominal (BET) specific surface area of 200 m²/g.The opacifier material had a nominal particle size such that 100% of thematerial passed through a 9 micron sieve.

As illustrated in FIG. 1, each aerated mixture 2 formed in a mixer 4 wasintroduced into a feed hopper 1 of a roller compactor apparatus 3, forexample a model FR compactor available from Turbo Kogyo Co. Ltd. ofJapan.

The roller compactor apparatus 3 comprised the feed hopper 1, anextrusion means in the form of a pair of opposed compression rollers 5,and screw conveyor means 7 for moving each mixture from the hopper tothe compression rollers. The walls of the screw conveyor means wereprovided with metallic porous membranes having pores with nominaldiameters approximately 15 microns.

The roller compactor apparatus also comprised a rotary chopper 9 and agranulator 11.

Each mixture was fed through a rotary valve (not shown) from the hopper1 to the screw conveyor means 7. The screw conveyor means 7 conveyedeach mixture at a first volumetric flow rate to the roller (shown inTable 1 hereinafter).

The screw conveyed mixtures were passed through the pair of compressionrollers. Each roller rotated about a substantially horizontal axis andthe rollers were arranged such that one roller was positioned parallelto, and vertically above, the other. The rollers were separated by a gapof nominally 1 mm. The pressure generated by the rollers on the mixtureswas selected to be either 5, 10 or 20 bar. The passage of each mixturefrom the hopper through the gap between the rollers resulted in themixtures being densified, compressed and extruded in the form ofsubstantially planar sheets of compressed thermal insulation material.The densified materials exited the rollers at the second volumetric flowrates shown in Table 1.

TABLE 1 First Second Ratio of Roller volumetric volumetric First to MixPressure flow rate flow rate Second flow No. (bar) (litres/hour)(litres/hour) rate 1 5 275 87 3.2:1 2 10 275 79 3.5:1 3 20 225 55 4.1:1

The action of the compression rollers on the mixtures caused the airpresent within the aerated mixtures to be forced out of the mixtures,potentially increasing the air pressure within the screw conveyor means.The potential increase in pressure in the screw conveyor means wassubstantially prevented by means of the porous membranes provided in thewalls which allowed air to be vented out of the screw conveyor means.

Each planar sheet of compressed thermal insulation material was thenpassed from the rollers 5, via deflecting means 15, through the rotarychopper 9 in which blades 17 provided on the rotary chopper 9 caused thecompressed material to be broken up into smaller pieces with a nominaldiameter in a range from 2 to 5 mm and a nominal thickness of 1 mm.

The smaller pieces of each thermal insulation material were passed intothe granulator 11. The granulator comprised a metal screen mesh 19 and arotor 21 positioned relative to the screen mesh. The screen mesh had anominal aperture size of 2.5 mm. The relative motion of the rotor to thescreen mesh caused the broken pieces of each thermal insulation materialprovided between the rotor and the mesh to be forced though apertures ofthe mesh to produce granular fibre-free microporous thermal insulationmaterial. Each granular fibre-free microporous thermal insulationmaterial 25 was retained in a collecting means 23. A sieve was used toremove granules of collected granular fibre-free microporous thermalinsulation material with a nominal size of less than 0.6 mm.

The granule size of each of the granular fibre-free microporous thermalinsulation materials was measured by sieve analysis, as known to aperson skilled in the art. The range of granule size for each mix wasfrom 0.25 mm to 2.5 mm.

Granular fibre-free microporous thermal insulation materials with agranule size of less than 0.6 mm were detected by the sieve analysis asthe granules of the materials underwent some break up due to handlingand the process of the sieve analysis itself.

The bulk density of each of the granular fibre-free microporous thermalinsulation materials was measured using apparatus known to a personskilled in the art. The bulk densities are shown in Table 2 hereinafter.

The tap density (otherwise known as the optimally settled density) ofeach of the granular fibre-free microporous thermal insulation materialswas determined by repeat tapping of a known mass of a sample of each ofthe insulation materials in a container of predetermined volume using anautomated tapping machine, known to a person skilled in the art, untilthe density of each of the materials underwent no further change. Thedensity at which no further change occurred following continued tappingcorresponded to the tap density of the material. The measured tapdensity of each of the granular fibre-free microporous thermalinsulation materials is shown in Table 2 below.

Each granular fibre-free microporous thermal insulation material wastested for thermal conductivity at a mean temperature of 400 degreesCelsius and at the tap density of the material, as determined by theabove method, using cylindrical cell thermal conductivity methods asknown by a person skilled in the art and as described in European FuelCell News, volume 8, number 2, July 2001. The results are shown in Table2 below.

The effect of temperature on each of the granular fibre-free microporousthermal insulation materials was also tested. A straight sided aluminacrucible was filled with a granular fibre-free microporous thermalinsulation material. Vibration was applied to the crucible during thefilling to produce a substantially consistent packing density of thegranular fibre-free microporous thermal insulation material within thecrucible. The granular fibre-free microporous thermal insulationmaterial was then heated at nominally 900 degrees Celsius for 24 hours.The height of the granular fibre-free microporous thermal insulationmaterial within the crucible was measured before and after heating andthe percentage difference in height was noted (see Table 2 below).

A negative value for the change in height indicates that the height ofthe granular fibre-free microporous thermal insulation material withinthe crucible after heating was less than the height before heating.

TABLE 2 Change in height of Bulk Tap Thermal heated Mix Density DensityConductivity material No. (kg/m³) (kg/m³) (W/mK) (Percent) 1 253 3500.0387 −1.4 2 277 406 0.0418 −1.8 3 325 450 0.0473 −1.6

EXAMPLE 2

Two granular fibre-free microporous thermal insulation materials (MixNos. 4 and 5) were made by mixing together mixtures of the microporousinsulating material and infrared opacifier described in Example 1.

Mix 4 was made by mixing together a mixture of nominally 50% dry weightof the microporous insulating material and 50% dry weight of infraredopacifier.

Mix 5 was made by mixing together a mixture of nominally 40% dry weightof the microporous insulating material and 60% dry weight of infraredopacifier.

Each mix was mixed to form an intimate, homogenous aerated mixture. Theaerated mixes had a bulk density of 80 kg/m³.

The mixes were introduced into the roller compactor apparatus asdescribed in Example 1 to produce granular fibre-free microporousthermal insulation materials essentially as described in Example 1.

The mixtures were conveyed by the screw conveyor 7 to the roller at thevolumetric flow rates shown in Table 3.

The pressure generated by the rollers on the mixtures was bar.

The densified material exited the rollers at the volumetric flow ratesshown in Table 3.

TABLE 3 First Second Ratio of Roller volumetric volumetric First to MixPressure flow rate flow rate Second flow No. (bar) (litres/hour)(litres/hour) rate 4 5 275 82 3.4:1 5 5 188 59 3.2:1

The bulk density, tap density, thermal conductivity and effect oftemperature were determined and measured as described in Example 1.

TABLE 4 Change in height of Bulk Tap Thermal heated Mix Density DensityConductivity material No. (kg/m³) (kg/m³) (W/mK) (Percent) 4 269 3900.0357 −1.8 5 256 420 0.0373 −1.7

EXAMPLE 3

A granular fibre-free microporous thermal insulation material (Mix No.6) was made by mixing together a mixture of nominally 85% dry weight ofa microporous insulating material, as described in Example 1, and 15%dry weight of infrared opacifier in the form of silicon carbide, gradeF1200D, available from ESK of Germany to form an intimate, homogenousaerated mixture. The aerated mix had a bulk density of 80 kg/m³.

The mix was introduced into the roller compactor apparatus as describedin Example 1 to produce a granular fibre-free microporous thermalinsulation material essentially as described in Example 1.

The mixture was conveyed by the screw conveyor 7 to the roller at avolumetric flow rate of 125 litres/hour.

The pressure generated by the rollers on the mixture was 5 bar.

The densified material exited the rollers at a volumetric flow rate of56 litres/hour. Consequently the ratio of first to second volumetricflow rates was 2.2:1.

The bulk density of the granular fibre-free microporous thermalinsulation material was measured to be 180 kg/m³.

The tap density of the granular fibre-free microporous thermalinsulation material was determined, as described in Example 1, to be 250kg/m³.

The granular fibre-free microporous thermal insulation material wastested for thermal conductivity as described in Example 1 and measuredto be 0.0374 W/mK.

The effect of temperature on the granular fibre-free microporous thermalinsulation material was also tested as described in Example 1. Thepercentage change in height of material following heating at nominally900 degrees Celsius for 24 hours was −1.6 percent.

EXAMPLE 4

A granular fibre-free microporous thermal insulation material (Mix No.7) was made by mixing together a mixture of nominally 35% dry weight ofa microporous insulating material, as described in Example 1, 25% dryweight of a microporous insulating material in the form of a hydrophobicfumed silica material available from Degussa AG under the RegisteredTrade Mark AEROSIL R974 and 40% dry weight of infrared opacifier, asdescribed in Example 1, to form an intimate, homogenous aerated mixture.The aerated mix had a bulk density of 80 kg/m³.

The mix was introduced into the roller compactor apparatus as describedin Example 1 to produce a granular fibre-free microporous thermalinsulation material essentially as described in Example 1.

The mixture was conveyed by the screw conveyor 7 to the roller at avolumetric flow rate of 188 litres/hour.

The pressure generated by the rollers on the mixture was 5 bar.

The densified material exited the rollers at a volumetric flow rate of54 litres/hour. Consequently the ratio of first to second volumetricflow rates was 3.5:1.

The bulk density of the granular fibre-free microporous thermalinsulation material was measured to be 276 kg/m³. The tap density of thegranular fibre-free microporous thermal insulation material wasdetermined, as described in Example 1, to be 420 kg/m³.

The granular fibre-free microporous thermal insulation material wastested for thermal conductivity as described in Example 1 and measuredto be 0.0337 W/mK.

The effect of temperature on the granular fibre-free microporous thermalinsulation material was also tested as described in Example 1. Thepercentage change in height of material following heating at nominally900 degrees Celsius for 24 hours was −1.3 percent.

EXAMPLE 5

Two granular fibre-free microporous thermal insulation materials (MixNos. 8 and 9) were made by mixing together mixtures of the microporousinsulating material and infrared opacifier described in Example 1 alongwith a particulate insulating filler material in the form of microngrade exfoliated vermiculite available from Hoben International.

Mix 8 was made by mixing together a mixture of nominally 57.5% dryweight of the microporous insulating material, 37.5% dry weight ofinfrared opacifier and 5% dry weight of vermiculite.

Mix 9 was made by mixing together a mixture of nominally 55% dry weightof the microporous insulating material, 35% dry weight of infraredopacifier and 10% dry weight of vermiculite.

Each mix was mixed to form an intimate, homogenous aerated mixture. Theaerated mixes had a bulk density of 80 kg/m³.

The mixes were introduced into the roller compactor apparatus asdescribed in Example 1 to produce granular fibre-free microporousthermal insulation materials essentially as described in Example 1.

The mixtures were conveyed by the screw conveyor 7 to the roller at thevolumetric flow rates shown in Table 5.

The pressure generated by the rollers on the mixtures was 5 bar.

The densified material exited the rollers at the volumetric flow ratesshown in Table 5.

TABLE 5 First Second Ratio of Roller volumetric volumetric First to MixPressure flow rate flow rate Second flow No. (bar) (litres/hour)(litres/hour) rate 8 5 188 65 2.9:1 9 5 200 66 3.0:1

The bulk density, tap density, thermal conductivity and effect oftemperature were determined and measured as described in Example 1.

TABLE 6 Change in height of Bulk Tap Thermal heated Mix Density DensityConductivity material No. (kg/m³) (kg/m³) (W/mK) (Percent) 8 230 3350.0382 3.0 9 242 342 0.0372 5.0

It was noted that with the addition of vermiculite, the height of thegranular fibre-free microporous thermal insulation materials made fromMix Nos. 8 and 9 increased following heating at nominally 900 degreesCelsius for 24 hours. The expansion of a granular fibre-free microporousthermal insulation material on heating has the beneficial effect ofcausing the insulation to more adequately fill any potential spaceswithin an area to be insulated which could provide a through-path forheat.

EXAMPLE 6

A granular fibre-free microporous thermal insulation material (Mix No.10) was made by mixing together a mixture of nominally 48% dry weight ofa microporous insulating material, 12% dry weight of a particulateinsulating filler material in the form of a volatilised silica material,grade VAW, available from RW Fuller of Germany Degussa AG and 40% dryweight of infrared opacifier to form an intimate, homogenous aeratedmixture.

The microporous insulating material and the infrared opacifier were asdescribed in Example 1.

The aerated mix had a bulk density of 80 kg/m³.

The mix was introduced into the roller compactor apparatus as describedin Example 1 to produce a granular fibre-free microporous thermalinsulation material essentially as described in Example 1.

The mixture was conveyed by the screw conveyor 7 to the roller at avolumetric flow rate of 250 litres/hour.

The pressure generated by the rollers on the mixture was 5 bar.

The densified material exited the rollers at a volumetric flow rate of70 litres/hour. Consequently the ratio of first to second volumetricflow rates was 3.6:1.

The bulk density of the granular fibre-free microporous thermalinsulation material was measured to be 286 kg/m³.

The tap density of the granular fibre-free microporous thermalinsulation material was determined, as described in Example 1, to be 395kg/m³.

The granular fibre-free microporous thermal insulation material wastested for thermal conductivity as described in Example 1 and measuredto be 0.0397 W/mK.

The effect of temperature on the granular fibre-free microporous thermalinsulation material was also tested as described in Example 1. Thepercentage change in height of material following heating at nominally900 degrees Celsius for 24 hours was −5.5 percent.

EXAMPLE 7

A granular fibre-free microporous thermal insulation material (Mix No.11) was made by mixing together a mixture of nominally 48% dry weight ofa microporous insulating material (described in Example 1), 12% dryweight of a microporous insulating material in the form of aprecipitated silica material, grade LS500, available from Degussa AG and40% dry weight of infrared opacifier (described in Example 1) to form anintimate, homogenous aerated mixture. The aerated mix had a bulk densityof 80 kg/m³.

The mix was introduced into the roller compactor apparatus as describedin Example 1 to produce a granular fibre-free microporous thermalinsulation material essentially as described in Example 1.

The mixture was conveyed by the screw conveyor 7 to the roller at avolumetric flow rate of 238 litres/hour.

The pressure generated by the rollers on the mixture was 5 bar.

The densified material exited the rollers at a volumetric flow rate of69 litres/hour. Consequently the ratio of first to second volumetricflow rates was 3.4:1

The bulk density of the granular fibre-free microporous thermalinsulation material was measured to be 276 kg/m³.

The tap density of the granular fibre-free microporous thermalinsulation material was determined, as described in Example 1, to be 380kg/m³.

The granular fibre-free microporous thermal insulation material wastested for thermal conductivity as described in Example 1 and measuredto be 0.0405 W/mK.

The effect of temperature on the granular fibre-free microporous thermalinsulation material was also tested as described in Example 1. Thepercentage change in height of material following heating at nominally900 degrees Celsius for 24 hours was −7.1 percent.

Granular fibre-free microporous thermal insulation material according tothe present invention has been described in which the infrared opacifiermaterial is either rutile (titanium dioxide) or silicon carbide. Itshould be appreciated that the infrared opacifier material could also beselected from other suitable materials, for example iron titanium oxide(for example ilmenite or leucoxene), zirconium silicate (zircon),zirconium oxide (zirconia), iron oxide (for example hematite), andmixtures thereof.

The fumed silica can have a specific surface area in a range from 50m²/g to 400 m²/g, preferably in a range from 180 m²/g to 230 m²/g.

In addition to the compositions described in the examples, it should beappreciated that granular fibre-free microporous thermal insulationmaterial in accordance with the present invention could consist of fumedsilica material in a range from 30 to 95% dry weight, infrared opacifierin a range from 5 to 70% dry weight, particulate insulating fillermaterial in a range from 0 to 50% dry weight, and binder material in arange from 0 to 5% dry weight.

The binder can be an organic binder, for example polyvinylalcohol, orcan be an inorganic binder, for example sodium silicate, potassiumsilicate and/or aluminium orthophosphate.

Although Example 5 describes the addition of a particulate insulatingfiller material in the form of vermiculite, it should be appreciatedthat the particulate insulating filler material could be perlite, flyashand/or volatilised silica (otherwise known as arc silica or silicafume).

The bulk density of granular fibre-free microporous thermal insulationmaterial in accordance with the present invention can be in a range from180 to 350 kg/m³.

The tap density of the granular fibre-free microporous thermalinsulation material can be in a range from 250 to 450 kg/m³.

Although the examples have described the use of a roller compactorapparatus, it should be appreciated that any apparatus which enables airto be vented from an aerated mixture to provide a compressed materialwhich is granulated can be used.

Although the examples describe the extrusion means of the rollercompactor apparatus exerting a pressure on the intimate aerated mixturein a range from 5 to 20 bar, it should be appreciated that a pressure ina range from 2.5 to 20 bar could be applied. The preferred range ofpressure is from substantially 5 to substantially 10 bar.

Although the diameters of the pores of the porous membrane are describedas being approximately 15 micron, it should be appreciated that thepores could have diameters in a range from 5 to 50 micron.

It should be appreciated that the first volumetric flow rate can be in arange from 2.0 to 4.5 times the second volumetric flow rate. The firstvolumetric flow rate can be in a range from 100 to 300 litres/hour,preferably in a range from 125 to 280 litres/hour. The second volumetricflow rate can be in a range from 25 to 90 litres/hour, preferably in arange from 50 to 90 litres/hour.

Although in the examples the means of compacting the material isdescribed as a pair of opposed rollers, it should be appreciated thatother compression means can be used, for example compression between asingle roller and a substantially flat substrate or between a pair ofsubstantially parallel compression faces.

The compacted material has been described as being in sheet form. Itshould be appreciated that the compacted material used to form thegranular fibre-free microporous thermal insulation can be of otherlaminar forms, for example strips.

Although a rotary chopper has been described in the examples to break upthe compressed material prior to granulation, it should be appreciatedthat other means, for example slicing means, could be used to break upthe material. It should also be appreciated that the compressed materialcan be fed directly into the granulator without first being broken upinto smaller pieces.

Granular fibre-free microporous thermal insulation made in accordancewith the present application has a thermal conductivity which isconsiderably lower than vermiculite or granulated mixtures of clay andcalcined diatomaceous earth.

At a mean temperature of 400 degrees Celsius, granular fibre-freemicroporous thermal insulation in accordance with the present inventionhas a thermal conductivity lower than expanded vermiculite at its tapdensity.

Granular fibre-free microporous thermal insulation made in accordancewith the present application has a height shrinkage which isconsiderably lower than granular microporous aerogel materials.

1. A granular fibre-free microporous thermal insulation material, having a thermal conductivity less than 0.05 W/mK, when measured at a mean temperature of 400 degrees Celsius and at the tap density of the material, and a shrinkage of not more than 10%, which is free flowing and consists of granules formed from an intimate mixture of: 30-95% dry weight microporous insulating material; 5-70% dry weight infrared opacifier material; 0-50% particulate insulating filler material; and 0-5% binder material.
 2. A thermal insulation material as claimed in claim 1, wherein the thermal insulation material has substantially the following composition: 40-85% dry weight microporous insulating material; 15-60% dry weight infrared opacifier material; 0-50% particulate insulating filler material; and 0-5% binder material.
 3. A thermal insulation material as claimed in claim 1, wherein a granule size of the granular fibre-free microporous thermal insulation material is in a range from 0.25 mm to 2.5 mm.
 4. A thermal insulation material as claimed in claim 1, wherein a bulk density of the granular fibre-free microporous thermal insulation material is in a range from 180 to 350 kg/m³.
 5. A thermal insulation material as claimed in claim 1, wherein the tap density of the granular fibre-free microporous thermal insulation material is in a range from 250 to 450 kg/m³.
 6. A thermal insulation material as claimed in claim 1, wherein the opacifier material is selected from titanium dioxide, iron titanium oxide, zirconium silicate, zirconium oxide, iron oxide, silicon carbide, and mixtures thereof.
 7. A thermal insulation material as claimed in claim 1, wherein the microporous insulating material comprises silica. 8.-12. (canceled)
 13. A thermal insulation material as claimed in claim 1, wherein the particulate insulating filler material is selected from vermiculite, perlite, flyash, volatilised silica, and mixtures thereof.
 14. A thermal insulation material as claimed in claim 1, wherein the binder comprises an organic binder.
 15. A thermal insulation material as claimed in claim 14, wherein the organic binder comprises polyvinylalcohol.
 16. A thermal insulation material as claimed in claim 1, wherein the binder comprises an inorganic binder.
 17. A thermal insulation material as claimed in claim 16, wherein the inorganic binder is selected from sodium silicate, potassium silicate, aluminium orthophosphate, and mixtures thereof.
 18. A method of manufacturing a granular fibre-free microporous thermal insulation material, having a thermal conductivity of less than 0.05 W/mK, when measured at a mean temperature of 400 degrees Celsius and at the tap density of the material, and a shrinkage of not more than 10%, which is free flowing and consists of granules formed from a mixture of 30-95% dry weight microporous insulating material, 5-70% dry weight infrared opacifier material, 0-50% particulate insulating filler material, and 0-5% binder material comprising the steps of: mixing together the microporous insulating material and the infrared opacifier material to form an intimate aerated mixture with a first density; conveying the intimate mixture at a first volumetric flow rate to an extrusion means (5); extruding the intimate mixture as a compressed material with a second density greater than the first density at a second volumetric flow rate lower than the first volumetric flow rate; venting a proportion of air from the aerated intimate mixture through a porous membrane to relieve pressure generated within the intimate mixture due to the change from the first volumetric flow rate to the second volumetric flow rate; and granulating the compressed material.
 19. A method according to claim 18, wherein the first volumetric flow rate is in a range from 2.0 to 4.5 times the second volumetric flow rate.
 20. A method according to claim 18, wherein the first volumetric flow rate is in a range from 100 to 300 litres/hour.
 21. (canceled)
 22. A method according to claim 18, wherein the second volumetric flow rate is in a range from 20 to 90 litres/hour.
 23. (canceled)
 24. A method according to claim 18, wherein the method includes the step of conveying the intimate mixture to the extrusion means (5) by means of a screw conveyor (7).
 25. A method according to claim 18, wherein the method includes the step of extruding the intimate aerated mixture by at least one roller (5).
 26. A method according to claim 25, wherein the intimate aerated mixture is extruded by a pair of opposing rollers (5).
 27. A method according to claim 18, wherein a pressure in a range from 2.5 to 20 bar is exerted to extrude the intimate aerated mixture.
 28. (canceled)
 29. A method according to claim 18, wherein the porous membrane is metallic and has pores with nominal diameters in a range from 5 to 50 microns.
 30. (canceled)
 31. A method according to claim 18, wherein the compressed material is in the form of a sheet of compressed material.
 32. A method according to claim 18 and including the step of breaking up the compressed material into smaller pieces prior to granulation.
 33. A method according to claim 32, wherein the compressed material is broken up by rotary chopping.
 34. A method according to 18, wherein granulation of the compressed material includes the step of forcing material through apertures in a mesh (19) using a rotor (9). 35.-51. (canceled) 